Asiatic Jasmine Dying in a Circle

My Asiatic jasmine ground cover, of which I have 1500+/- square ft., started dying about 6 months ago in a small circle and now about 20 foot diameter. I have been treating it with several things (Sevin, Mole and Vole, Insect killer, Systemic weed killer, Bayer Advanced insect killer, Malathion spray, etc.). It has slowed down somewhat but it keeps creeping larger. This ground cover was planted some 15 years ago and until this have had no problem at all. If you have any suggestions, please let me know.

I believe that your asiatic jasmine is afflicted with rhizoctonia large patch disease which causes dieback in circular patterns. For more information on large patch disease and how to treat it, please visit the following link: